Well, if you can wait for delivery (because its in the UK), one of the best kits out there is one by Earthshine Electronics:
http://www.earthshineelectronics.com/10-arduino-duemilanove-compatible-starter-kit.html
It costs £49.99 (~$80.71 USD).
At the very least, download the manual for the kit, which is one of the best beginner books out there for the Arduino:
http://www.earthshineelectronics.com/files/ASKManualRev4.pdf
...and the code:
http://www.earthshineelectronics.com/files/EDASKCode.zip
